None.
None.
None.
This invention relates to materials and processes for producing cellulose products and for protecting cellulose matter from fire, deterioration, and the like.
Application of sodium silicate and a fire retardant to cellulose material, of which wood and wood products are typical, in order to protect the material from fire and from deterioration through fungus, rot, and insect attack, for example, is a well-known practice. One illustrative technique first exposes the wood to a vacuum. The wood then is subjected to a mixture of sodium silicate and a fire retardant mixture under a pressure of 300 pounds per square inch. Another process coats a wood surface with an alkali metal silicate and a carbonate in order to preserve the wood and to provide fire protection. And still another process provides for the application to plywood of an aqueous solution that combines ten materials, including sodium bicarbonate and sodium silicate.
None of these treatment compositions or processes, however, are entirely satisfactory. Illustratively, the sodium silicate, which is a primary protection for cellulose materials from deterioration through fungus and insect attack, if only superficially applied to the wood, swiftly erodes. Or if the sodium silicate penetrates the wood to some depth, subsequent immersion in water, for example, causes the sodium silicate to leach out of the cellulose structure, thus leaving the wood as unprotected as if it had not been treated at all.
Cellulose, or wood product manufacture, such as the production of chip board, particle board (e.g. oriented strand board) and plywood, require an adhesive to bond together the chips, particles or layered plies into a solid structure. Ordinarily, a resinous adhesive is used for this purpose.
These adhesives, however, are subject to a number of disadvantages. Many of these adhesives are, for example, costly; produce undesirable formaldehyde emissions; and are environmentally harmful.
There also is the continuing and unsatisfied long-term need, described above, to protect the cellulose material in the product from rot, fungus and insect attack.
Consequently, there is a need for an improved wood preservative and fire retardant treatment technique for cellulose materials and an inexpensive wood product adhesive that enjoys chemical compatibility with the environment, the preservatives and the fire retardant.
These and other problems that have characterized the prior art are overcome, to a large extent, through the practice of the invention. For example, first immersing, spraying or subjecting to a vacuum and then pressure treating the cellulose material with a wood preservative, e.g. an aqueous solution of sodium silicate, that has been heated to about 180xc2x0 F. not only establishes the protection from deterioration that is inherent in the preservative, but, because of the high temperature of the preservative during application, also kills bacteria that are harmful to the cellulose.
Subsequently, the cellulose matter that has been treated with the heated preservative is allowed to cool to a suitable temperature of about 112xc2x0 F., or less. A solution of sodium bicarbonate is then applied by immersion; vacuum and pressure treatment; or sprayed onto the cellulose matter.
The product, heated to about 112xc2x0 F. toward the end of the sodium bicarbonate treatment step, moreover, causes the treating substances to polymerize into an insoluble gel, a condition that enhances the insolubility of the preservative and the fire retardant that have been absorbed within the wood thereby significantly increasing the duration of the product""s protection.
The insoluble gel prevents the preservative from erosion or from leaching out of the cellulose matter as a consequence of subsequent exposure to water, and the like. The gel also imparts a fire retardant feature, in that the sodium bicarbonate, in the gel, on exposure to a temperature of about 112xc2x0 F. or more, evolves a carbon dioxide gas that retards and suppresses combustion.
The invention also contemplates other methods for applying a fire retardant to the cellulose material. For example, after the cellulose material has been impregnated with hot sodium silicate preservative solution through the illustrative combination of vacuum and pressure treatment described above, a carbon dioxide gas then is applied directly to the material. The carbon dioxide gas forms, with the sodium silicate, a gel that not only prevents the sodium silicate from eroding or leaching out of the cellulose matrix, but also enables carbon dioxide gas to discharge from the gel and matrix, in order to suppress combustion.
With respect to cellulose product manufacture, moreover, chips, particles or individual plies are immersed, sprayed or vacuum and pressure treated, as described above, with a suitable preservative compound. The chips, particles or plies, moistened through the preservative treatment, are then coated, preferably by spraying the moistened chips or the like, with a suitable, environmentally acceptable adhesive, e.g. soybean or cottonseed meal or protein. The coated material is then heated to a temperature of not less than 212xc2x0 F. and pressed, depending on the product, to production pressure that is customary within the industry to form the specific product. Thus, in accordance with another feature of the invention, the comminuted meal provides an inexpensive and environmentally acceptable adhesive or bonding agent.
The process steps of immersion, spraying or vacuum and pressure treatment are, from the standpoint of the invention, essentially interchangeable. Consequently, for the purpose of this description and the appended claims, the word xe2x80x9cprocessing,xe2x80x9d as used herein, is limited to and encompasses the steps either of immersion; or spraying; or vacuum and pressure treatment, unless stated otherwise in this text. Thus, for example, it is within the scope of the invention to apply the preservative to the cellulose material through immersion and to apply the fire retardant sodium bicarbonate through spraying or vacuum and pressure treatment. The sodium silicate preservative, moreover, can be applied to the cellulose material through, for instance, spraying or vacuum and pressure treatment with the sodium bicarbonate added by means of immersion.
With respect to pressure treatment, and entirely independent of and separate from any particular preservative or fire retardant, it has been found that reagent penetration, absorption, and accumulation within the cellulose structure is markedly improved by varying the pressure that is applied to the cellulose material that is being treated. Further in this same connection, by cycling the pressure of, for example, an aqueous solution of sodium silicate that is applied to a wood product through a range of pressures between 250 pounds per square inch (psi) in one or more cycles, mineral deposits in the wood are loosened, enabling more wood preservative, fire retardant and the like to be absorbed within the wood structure.
These and other features and advantages of the invention will be understood in more detail through the following description of preferred embodiment of the invention when taken with the figures of the drawing. The scope of the invention, however, is limited only through the claim appended hereto.